FIG. 5 is a diagram schematically showing a configuration of a conventional spectroscopic device. Here, as an example of the spectroscopic device, a PDA (photodiode array) absorbance detector, for a liquid chromatograph, including a multiple wavelength detection function will be described.
As shown in FIG. 5, the spectroscopic device includes a lamp house 1, and a spectrometer 3.
A light source 5 is provided inside the lamp house 1. Light emitted from the light source 5 is radiated on the spectrometer 3 via an aperture plate (not shown).
The spectrometer 3 is provided with, in the order of passing of light, an aperture plate (not shown), a focusing mirror 7, a flow cell 9, a focusing mirror 11, a slit 13, a concave diffraction grating 15, and a photodiode array 17.
The lamp house 1 and the spectrometer 3 are arranged with a spacer 19 having an opening for light transmission therebetween.
Also, a fan 21 for cooling the lamp house 1 is provided to the spectroscopic device.
The lamp house 1 and the fan 21 are provided to suppress a change in the amount of light emission of the light source 5 due to a change in the ambient temperature of the device. Generally, the amount of light emission of the light source 5 changes according to a change in the temperature of the light source 5. When the amount of light of the light source 5 changes, the output value of the photodiode array 17 changes, and thus, high sensitivity measurement is possibly prevented. Accordingly, to prevent the output value of the photodiode array 17 from changing due to a change in the ambient temperature of the device, the light source 5 is accommodated in the lamp house 1 whose heat capacity is high to a certain degree and the lamp house 1 is cooled by the fan 21 with certain air volume so as to radiate heat, and the temperature of the light source 5 is thus not easily changed even if the ambient temperature of the device changes.
The spectroscopic device shown in FIG. 5 is a device for measuring an absorption spectrum of an analysis sample flowing into the flow cell 9, by emitting light radiated by the light source 5 on the flow cell 9 and causing the light which has passed through the flow cell 9 to be dispersed on the photodiode array 17 by the diffraction grating 15.
According to this spectroscopic device, when the light source 5 is illuminated from a light-off state, the spectrometer 3 is thermally expanded due to the heat generated by the light source 5, and the optical axis changes inside the spectrometer 3. Because of this influence, stabilization of the baseline of a chromatogram after the lighting of the light source 5 takes time.